Polymeric sulfonium salt photoinitiators

ABSTRACT

The invention is a polymeric photoinitiator having the formula: ##STR1## wherein n=10 to 50; each of a and b may be 0-4 while c is 0-5; A is an alkyl or aryl group; X is an anion; and each of R, R&#39;, and R&#34; is independently H or one or more groups substituted onto the respective phenyl moieties. The substituted groups are independently selected from various kinds of groups excluding basic groups such as amino groups. Preferably, they are a hydrogen atom, halogen atom (e.g., F, Cl, Br, and I) , nitro group, alkoxy group (e.g. , CH 3  O-- and C 2  H 5  O--) , C 1  -C 18  aliphatic group (e.g., hydrocarbon group such as CH 3  --, C 2  H 5  --, and (CH 3 ) 2  CH--; cyclic hydrocarbon group such as cyclohexyl group; and those which contain a heteroatom in the main chain or substituent group. The substituted groups may also be a C 1  -C 18  aliphatic group having at least one hydroxyl group or a C 3  -C 19  aliphatic group having a group of --OCH 2  CH 2  O--. The invention also comprises a method of synthesizing this polymer and adhesive compositions and computer components using and made with the polymeric photoinitiator of the invention. The invention also comprises a method of reducing outgassing from the component parts of data storage systems.

This is a division of application Ser. No. 08/455,218, filed May 31,1995, now U.S. Pat. No. 5,550,171 which application is incorporatedherein by reference.

FIELD OF THE INVENTION

Generally, the invention relates to sulfonium salt photoinitiators. Morespecifically, the invention relates to polymeric sulfonium saltphotoinitiators which are preferably used in information storage andretrieval devices such as data storage systems and data storage disks.

BACKGROUND OF THE INVENTION

Photoinitiator chemicals are those compounds which mediate, facilitateor otherwise cause those reactions which occur during the curing of anadhesive. Curing is a chemical phenomenon which occurs when certainatomic bonds are broken and reformed to create a compositional formwhich cannot be recast through the application of heat. These adhesivesare generally regarded as "thermosetting" and are most useful in thecreation of a strong, heat resistant, rigid adhesive bond. Through theapplication of ultraviolet energy, a photoinitiator constituentfacilitates the reformation of chemical bonds in a thermoset adhesive tocure the adhesive.

One application for photoinitiator cured thermoset adhesives is in theassembly of component parts used in data storage and retrieval systemssuch as CD-ROM technology and hard disk storage technology. Themanufacture of hard disk drives involves the use of sundry adhesivesspanning numerous applications. Due to the automated nature of the harddrive assembly process, rapid adhesive tack time is of paramountimportance. In order to accommodate such process requirements,photosensitive adhesives are often the material of choice. Among thisclass of adhesives, photosensitive, epoxy-based formulations are oftenselected due to their rapid fixture times, appreciable dark reaction,and excellent physical properties.

During the manufacture of hard disk drives, adhesives are used forsundry assembly applications. Volatile compounds from the adhesives havebeen known to deposit on the disk surface resulting in head/diskinterface failures. These compounds are typically low molecular weightentities that readily diffuse through the bulk of the adhesive andsubsequently effuse into the disk environment. Low molecular weightphotoinitiator compounds are exemplified by Crivello et al U.S. Pat. No.4,136,102 and 4,161,478 which each teach onium salt-type initiators ofphosphorous, arsenic, and antimony. Crivello teaches in each of thesepatents that the onium salts can be employed as cationic photoinitiatorswhen used with a variety of organic resins.

Smith et al, U.S. Patent No. 4,173,476 also teaches salt complexes whichmay be used as photoinitiators and epoxy compositions. The disclosedcompounds are triarylsulfonium complex salts having a discrete molecularweight. Crivello et al, U.S. Pat. No. 4,442,197 also teachesphotocurable compositions. The disclosed compositions are described asdialkylphenacyl sulfonium salts or hydroxyaryldialkyl sulfonium salts ofa discrete molecular weight. These compounds are polymerizable intoepoxy resins through the use of ultraviolet light at a wave lengthgreater than 300 nm.

Chang U.S. Pat. No. 4,197,174 teaches a method for producingbis-[4(diphenylsulfonio)phenyl] sulfide bis-MX₆ initiators which areuseful in the cationic polymerization of monomer formulations. Hereagain, the disclosed compositions are polymerized into epoxycompositions through the application of ultraviolet energy.

Iyer, U.S. Pat. No. 4,400,541 disclosesbis-(diphenylsulfoniophenyl)-sulfide bis-chloride salts again ofdiscrete molecular weight which are used as starting materials for themanufacture of other salts which has utility as catalyst for curingultraviolet activated coating compositions. Angelo et al, U.S. Pat. No.5,047,568 teaches sulfonium salts having a discrete molecular weightwhich may be used as photoinitiators for various adhesives.

However, the use of these photoinitiators does not alleviate problemswhich occur, especially in disk drive assemblies. After assembly,machines carrying disk drive units may be shipped to any number oflocations in the world and subsequently stored. Often times, and in mostcases, storage conditions may vary radically and defy control by theinitial manufacturer. Conditions of high temperature and high humidityare more the rule than the exception in many countries. In suchconditions, disk drives have a tendency to film due to many of thechemicals present in the disk drive environment.

A large body of evidence exists implicating various compounds (e.g.,silicones and acrylates) in head/disk interface failures. Trial andanalysis over time has illustrated that the composition of the filmwhich forms on disk drives is corrosion and has a high concentration ofsulphur. The use of sulfonium salts such as those found disclosed in thepatents cited above leads to low molecular weight volatile species whichoutgas and deposit upon the disk drive to form these corrosive films.

Therefore, there is a need in the art for photoinitiator compounds andpolymer systems which will effectively cure adhesives to a desired bondand which will not outgas low molecular weight constituents which, inturn, will corrode disk drive mechanisms or other component parts.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention there is provided apolymeric photoinitiator having the formula: ##STR2## wherein n=10 to150; each of a and b are 0-4 and c is 0-5; A is a branched or unbranchedalkyl or a substituted or unsubstituted aryl; X is an anion; and each ofR, R', R", and R'" is H or one or more groups substituted onto therespective phenyl. The substituted group is independently selected fromvarious kinds of groups excluding basic groups such as amino groups.Preferably, they are a hydrogen atom, halogen atom (e.g., F, Cl, Br, andI), nitro group, alkoxy group (e.g., CH₃ O-- and C₂ H₅ O--) , C₁ -C₁₈aliphatic group (e.g., hydrocarbon group such as CH₃ --, C₂ H₅ --, and(CH₃)₂ CH--); cyclic hydrocarbon group such as cyclohexyl group; andthose which contain a heteroatom in the main chain or substituent group.Each of R, R', and R" may also be a C₁ -C₁₈ aliphatic group having atleast one hydroxyl group or a C₃ -C₁₉ aliphatic group having a group of--OCH₂ CH₂ O--.

In accordance with another aspect of the invention, there is provided anadhesive composition comprising the photoinitiator of the invention.

In accordance with a further aspect of the invention, there is provideda data storage system assembled using adhesives cured with thephotoinitiator of the invention.

In accordance with an additional aspect of the invention, there isprovided a method of synthesizing the polymeric photoinitiator of theinvention.

The polymeric sulfonium salt photoinitiators have lower volatility andless tendency to outgas volatile compounds.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top perspective view of a data storage system with its upperhousing cover removed; and

FIG. 2 is a side plan view of a data storage system comprising aplurality of data storage disks.

DETAILED DISCUSSION OF THE CLAIMED INVENTION

Accordingly, the invention comprises a polymeric photoinitiator, and useof the polymeric photoinitiator in various adhesive compositions, andproducts resulting therefrom.

A. The Polymer

Generally, the polymeric photoinitiator of the invention has thefollowing composition: ##STR3## wherein n=10 to 150; each of a and b are0-4 and c is 0-5; A is a branched or unbranched alkyl or a substitutedor unsubstituted aryl; X is an anion; and each of R, R', and R" is H orone or more groups substituted onto the respective phenyl. Thesubstituted groups (r, R', and R") are independently selected fromvarious kinds of groups excluding basic groups such as amino groups.Preferably, they are a hydrogen atom, halogen atom (e.g., F, Cl, Br, andI), nitro group, alkoxy group (e.g., CH₃ O--and C₂ H₅ O--), C₁ -C₁₈aliphatic group (e.g., hydrocarbon group such as CH₃ --, C₂ H₅ --, and(CH₃)₂ CH--; cyclic hydrocarbon group such as cyclohexyl group; andthose which contain a heteroatom in the main chain or substituent group(e.g., ##STR4## or substituted or unsubstituted phenyl group, phenoxygroup, or thiophenoxy group.

Each of R, R', and R" may also be independently a C₁₋₁₈ aliphatic grouphaving at least one hydroxyl group such as a monoalcohol and polyalcoholrepresented by, for example, --CH₂ OH, --CH₂ CH₂ OH, --O--CH₂ CH₂ --CH₂CH₂ --OH, --SCH₂ CH₂ OH, ##STR5##

Each of R, R', and R" may also be a C₃₋₁₉ group having at least onegroup of --OCH₂ CH₂ O--independently a CH₂ O--CH₂ --CH₂ --O--CH₃,##STR6##

Preferably, each of R, R', and R" may independently be a linear orbranched C₁₋₄ alkyl group such as methyl, ethyl, propyl or butyl; analkoxy group such as those with ester, ether, or carboxyl,functionality; and hydrogen.

In turn, A may be a substituted or unsubstituted aryl or a linear orbranched alkyl. Representative groups include linear or branched C₁₋₆alkyl, as well as alkoxy including C₁₋₆ symmetric or symmetric ethergroups. Representative aryl groups include unsubstituted phenyl orphenyl substituted at any of meta, para, or ortho positions. Any of R,R', and R" (if A is an aryl group) may be meta, ortho, or para directedrelative to the carbon-sulphur bond in order to aid in synthesis of thepolymer.

B. Synthesis

The polymeric photoinitiator disclosed above results from polymerizationof various sulfonium monomers. This monomeric unit has the formula:##STR7## Ar of the above fused aromatic radical that is selected fromthe group of naphthyl, anthracyl, peryl, and pyryl. R₁ is a divalentbridge selected from the group of alkylene and alkenylene, alkylene andalkenylene chains broken with an oxygen atom; and substitutedderivatives of the above chains. The substituted derivatives are thosehaving pendent from the chain a hydroxyl group. R₁ usually containsabout 1-10 carbon atoms and preferably about 1-4 carbon atoms.

Examples of specific R₁ bridges include methylene, ethylene, propylene,isopropylidene, butylene, isobutylene, oxymethylene, oxypropylene, and3-hydroxy-1-oxybutylene.

Each R₂ and R₃ is individually an alkyl, aryl, substituted aryl,alkaryl, or aralkyl group, provided that not more than one of R₂ and R₃is an alkyl group. Generally, the alkyl groups contain 1-12 carbon atomsand preferably 1-4 carbon atoms, examples of which are methyl, ethyl,propyl, isopropyl, and butyl. The aryl groups can contain 6-12 carbonatoms and include phenyl, biphenyl, and naphthyl. The substituted arylgroups are generally those substituted with one of the groups of OH,OR', NH₂, NR'R" wherein each R' and R" is individually an alkyl groupcontaining generally 1-4 carbon atoms, including methyl and ethyl. Thealkaryl groups generally contain about 1-18 carbon atoms and preferablyabout 7-10 carbon atoms and include phenyl, and ethylbenzyl. The aralkylgroups usually contain from about 7-18 carbon atoms and preferably fromabout 7-10 carbon atoms and include tolyl and xylol. X⁻, in the aboveformula is a non-nucleophilic anion which can be SbF⁻ ₆, PF⁻ ₆, AsF⁻ ₆,BF⁻ ₄, CF₃ SO⁻ ₃, or ClO⁻ ₄.

Synthesis of the polymer of the invention may be undertaken over severaldiscrete steps. Generally, the first portion of the synthesis is theformation of a sulfonium salt from reaction of sulfone such as a diarylsulfone or preferably an alkyl diaryl sulfone with a diaryl sulfide.This reaction may be completed using equivalent mole ratios of eachprecursor compound. Preferably, the reaction is undertaken in a cooledenvironment, in the presence of an acid such as methane sulfonic acid.The reaction should be continued for a time ranging from 20 hours to 30hours. After this time, the reaction product may be extracted over anacidic aqueous/organic interface to purify and concentrate the product.The organic layer may be dried over anhydrous sodium sulfate to providea residue which may be purified by recrystallization with ether. Thereaction scheme is shown in equation [I] below. ##STR8##

As shown in equation [I], the sulfone methyl group may also be any C₂₋₆linear or branched alkyl group or any substituted or unsubstitutedphenyl group.

In the next step of the synthesis, an aromatic catenated sulfide isproduced by subjecting the sulfonium salt produced in the reaction shownin equation [I] to a nucleophile. A nucleophile, such as pyridine,strips the pendent alkyl or aryl group from the sulfonium salt producinga catenated sulfide. The reaction is undertaken by placing the sulfoniumsalt into a nucleophilic solvent with mixing. The temperature of themixture may be slowly increased to 100° C. and the reaction continuedfor 10 minutes to 20 minutes. The resulting product may then beextracted, purified, and dried by means known to those of skill in theart. The reaction scheme is shown below in equation [II]. ##STR9##

As shown in equation [II], the sulfonium salt has been demethylated.Here again, the reaction of equation [II] may be to dealkylate orarylate the sulfonium salt as indicated earlier.

The precursor to the polymer of the invention, an aromatic sulfoxide,may then be produced from the catenated aromatic sulfide. In thisinstance, the catenated aromatic sulfide is exposed to an equimolarconcentration of oxidizing agent such as bromine, or hydrogen peroxide(30 wt-%), sodium periodate, tert butoxy chloride, sodium perborate, orany suitable peracid in the presence of a suitable buffer such as sodiumbicarbonate and water. Additionally, various compounds may be used toensure adequate solubility of precursors and, in turn, full reaction.The product may then be extracted, purified and dried by means known tothose of skill in the art. The reaction scheme is shown below inequation [III]. ##STR10##

The final step in the synthesis is the polymerization of the aromaticsulfoxide, see equation [IV] below. To polymerize the sulfoxide, anelectrophile, such as an acid, is used to protonate the sulfoxide andstrip the oxygen from the sulfur atom in the form of water. At the sametime, an electrophile should be used which will not effect the anionicspecies [X⁻ ] so that this anion remains large and non-nucleophilic.Appropriate electrophiles include hexafluorophosphoric acid, hexafluoroarsenic acid (HAUF₆), hexafluoroantimonic acid, or trifluoromethanesulfonic acid. The viscosity of the reaction mixture gradually increasesduring polymerization. After precipitation in water, the poly(sulfoniumcation) is quantitatively isolated as a resin having the empiricalformula, C₁₈ H₁₄ S⁺ ₂.

The resulting polymer has a molecular weight which ranges from about 10⁴to 10 ⁵. ##STR11##

Method of Use

The photoinitiator of the invention may be used in any number of formsincluding neat, in solution, or in the intended adhesive. The polymer ofthe invention when used as a photoinitiator, are generally employed inthe adhesive in amounts up to about 5 wt-% based upon the material beingpolymerized and preferably from about 2 wt-% to about 3 wt-%.

When present in solution, the polymeric photoinitiator of the inventionhas a concentration of from about 20 wt-% to 50 wt-%, and morepreferably from about 30 wt-% to about 50 wt-%, and most preferably fromabout 40 wt-% to about 50 wt-%. Appropriate solvent systems for thepolymer of the invention are those which have a high solubilityparameter, (22 MPa⁰.5 or greater) such as gamma butyrolactone, propylenecarbonate, dimethylsulfoxide, N-methylpyrollidone, dimethylformamide, ormixtures thereof. In use, the polymeric photoinitiator is mixed with thechosen adhesive, applied to the substrate of choice and exposed to U.V.energy having a wavelength of about 200-500 μm, and preferably about254μm or about 365 μm in accordance with methods known to those of skillin the art.

The polymers of the present invention can be used as photoinitiators forcationic polymerization such as polymerizations of epoxy polymer,phenolplast, amino plast, polyvinylacetyls, cyclic ethers, and cyclicesters such as those disclosed in U.S. Pat. No. 5,047,568 issued Sep.10, 1991 to Angelo et al, which is incorporated herein by reference.

In its most preferred mode, the polymeric photoinitiator of theinvention may be used to cure epoxy resins. Typical examples of epoxypolymers include the epoxidized novolak polymers and the polyepoxidesfrom halo-epoxy alkanes such as epichlorohydrin and a polynucleardihydric phenol such as bisphenol A. Mixtures of epoxides can be usedwhen desired.

The epoxidized novolak polymers are commercially available and can beprepared by known methods by the reaction of a thermoplastic phenolicaldehyde of a phenol with a halo-epoxy alkane. The phenol can be amononuclear or polynuclear phenol.

Examples of mononuclear phenols have the formula: ##STR12##

Hydrocarbon-substituted phenols having two available positions ortho orpara to a phenolic hydroxy group for aldehyde condensation to providepolymers suitable for the preparation of epoxy novolaks include o- andp-cresols, o- and p-ethyl phenols, o- and p-isopropyl phenols, o- andp-tert-butyl phenols, o- and p-secbutyl phenols, o- and p-amyl phenols,o- and p-octyl phenols, o- and p-nonyl phenols, 2,5-xylenol,3,4-xylenol, 2,5-diethyl phenol, 3,4-diethyl xylenol, 2,5-diisopropylphenol, 4-methyl resorcinol, 4-ethyl resorcinol, 4-isopropyl resorcinol,4-tert-butyl resorcinol, o- and p-benzyl phenol, o- and p-phenethylphenols, o- and p-phenyl phenols, o- and p-tolyl phenols, o- and p-xylolphenols, o- and p-cyclohexyl phenols, o- and p-cyclopentyl phenols,4-phenethyl resorcinol, 4-tolyl resorcinol, and 4-cyclohexyl resorcinol.

Various chloro-substituted phenols which can also be used in thepreparation of phenol-aldehyde resins suitable for the preparation ofthe epoxy novolaks include o- and p-chloro-phenols, 2,5-dichloro-phenol,2,3-dichloro-phenol, 3,4-dichloro-phenol, 2-chloro-3-methyl-phenol,2-chloro-5-methyl-phenol, 3-chloro-2-methyl-phenol,5-chloro-2-methyl-phenol, 3-chloro-4-methyl-phenol,4-chloro-3-methyl-phenol, 4-chloro-3-ethyl-phenol,4-chloro-3-isopropyl-phenol, 3-chloro-4-phenyl-phenol,3-chloro-4-chloro-phenyl-phenol, 3,5-dichloro-4-methyl-phenol,3,5-dichloro-5-methyl-phenol, 3,5-dichloro-2-methyl-phenol,2,3-dichloro-5-methylphenol, 2,5-dichloro-3-methyl-phenol,3-chloro-4,5-dimethyl-phenol, 4-chloro-3,4-dimethyl-phenol,2-chloro-3,5-dimethyl-phenol, 5-chloro-2,3-dimethyl-phenol,5-chloro-3,5-dimethyl-phenol, 2,3,5-trichloro-phenol,3,4,5-trichloro-phenol, 4-chloro-resorcinol, 4,5-dichloro-resorcinol,4-chloro-5-methyl-resorcinol, 5-chloro-4-methyl-resorcinol.

Typical phenols which have more than two positions ortho or para to aphenolic hydroxy group available for aldehyde condensation and which, bycontrolled aldehyde condensation, can also be used are: phenol,m-cresol, 3,5-xylenol, m-ethyl and m-isopropyl phenols, m,m'-diethyl anddiisopropyl phenols, m-butyl-phenols, m-amyl phenols, m-octyl phenols,m-nonyl phenols, resorcinol, 5-methyl-resorcinol, 5-ethyl resorcinol.

Examples of polynuclear dihydric phenols are those having the formula:##STR13## wherein Ar is an aromatic divalent hydrocarbon such asnaphthylene and, preferably, phenylene: A₁ and A₂ which can be the sameor different are alkyl radicals, preferably having from 1 to 4 carbonatoms, halogen atoms, i.e., fluorine, chlorine, bromine, and iodine, oralkoxy radicals, preferably having from 1 to 4 carbon atoms; x and y areintegers having a value 0 to a maximum value corresponding to the numberof hydrogen atoms on the aromatic radical (Ar) which can be replaced bythe substituents and R₆ is a bond between adjacent carbon atoms as indihydroxydiphenyl or is a divalent radical including, for example:##STR14## and divalent hydrocarbon radicals, such as alkylene,alkylidene, cycloalphatic, e.g., cycloalkylene and cycloalkylidene,halogenated, alkoxy or aryloxy substituted alkylene, alkylidene andcycloaliphatic radicals, as well as alkarylene and aromatic radicalsincluding halogenated, alkyl, alkoxy or aryloxy substituted aromaticradicals and a ring fused to an Ar group; or R¹ can be polyalkoxy, orpolysiloxy, or two or more alkylidene radicals separated by an aromaticring, a tertiary amino group, an ether linkage, a carbonyl group or asulfur containing group such as sulfoxide, and the like.

Examples of other specific dihydric polynuclear phenols include, amongothers, the bis-(hydroxyphenyl) alkanes such as2,2'-bis-(4hydroxyphenyl)propane, 2,4'-dihydroxydiphenylmethane,bis-(2-hydroxyphenyl)methane, bis(4-hydroxyphenyl)methane,bis(4-hydroxy-2,6-dimethyl-3- methoxyphenyl)methane,1,1'-bis-(4-hydroxyphenyl) ethane, 1,2'-bis-(4-hydroxyphenyl)ethane,1,1'-bis-(4-hydroxy-2-chlorphenyl)ethane,1,1'-bis(3-methyl-4-hydroxyphenyl)ethane,1,3'-bis-(3-methyl-4-hydroxyphenyl)propane,2,2'-bis-(3-phenyl-4-hydroxyphenyl)propane,2,2'-bis-(3-isopropyl-4-hydroxyphenyl)propane,2,2'-bis(2-isopropyl-4-hydroxyphenyl)pentane, 2,2'-bis-(4-hydroxyphenyl)heptane, bis-(4-hydroxyphenyl)phenylmethane,bis-(4-hydroxyphenyl)cyclohexylmethane,1,2'-bis-(4-hydroxy-phenyl)-1,2'-bis-(phenyl)propane and2,2'-bis-(4-hydroxy-phenyl)-1-phenyl-propane; di(hydroxyphenyl) sulfonessuch as bis-(4-hydroxyphenyl)sulfone, 2,4'-dihydroxydiphenylsulfone,5'-chloro-2,4'-dihydroxydiphenyl sulfone, and5'-chloro-4,4'-dihydroxydiphenyl sulfone; di(hydroxyphenyl)ethers suchas bis-(4-hydroxy-phenyl)ether, the 4,4'-, 4,2'-, 2,2'-, 2,3'-,dihydroxydiphenyl ethers, 4,4'-dihydroxy-2,6-dimethyldiphenyl ether,bis-(4-hydroxy-3-isobutylphenyl) ether,bis-(4-hydroxy-3-isopropylphenyl)ether, bis-(4-hydroxy-3-chlorophenyl)ether, bis-(4-hydroxy-3-fluorophenyl) ether,bis-(4-hydroxy-3-bromophenyl)ether, bis-(4-hydroxynaphthyl)ether,bis-(4-hydroxy-3-chloronaphthyl)ether, bis-(2-hydroxydiphenyl)ether,4,4'-dihydroxy-2,6-dimethoxydiphenyl ether, and4,4'-dihydroxy-2,5-diethoxydiphenyl ether.

The preferred dihydric polynuclear phenols are represented by theformula: ##STR15## wherein A₁ and A₂ are as previously defined, x and yhave values from 0 to 4 inclusive and R₆ is a divalent saturatedaliphatic hydrocarbon radical, particularly alkylene and alkylideneradicals having from 1 to 3 carbon atoms, and cycloalkylene radicalshaving up to and including 10 carbon atoms. The most preferred dihydricphenol is bisphenol A, i.e. 2.24-bis(p-hydroxyphenyl)propane.

As condensing agents, any aldehyde may be used which will condense withthe particular phenol being used, including formaldehyde, acetaldehyde,propionaldehyde, butyraldehyde, heptaldehyde, cyclohexanone, methylcyclohexanone, cyclopentanone, benzaldehyde, and nuclearalkyl-substituted benzaldehydes, such as toluic aidehyde,naphthaldehyde, furfuraldehyde, glyoxal, acrolein, or compounds capableof engendering aldehydes such as para-formaldehyde, hexamethylenetetramine. The aldehydes can also be used in the form of a solution,such as the commercially available formaline. The preferred aldehyde isformaldehyde.

The halo-epoxy alkane can be represented by the formula: ##STR16##wherein X is a halogen atom (e.g., chlorine, bromine, and the like), pis an integer from 1-8, each R₂ individually is hydrogen or alkyl groupof up to 7 carbon atoms; wherein the number of carbon atoms in any epoxyalkyl group totals no more than 10 carbon atoms.

While glycidyl ethers, such as derived from epichlorohydrin, areparticularly preferred in the practice of this invention, the epoxypolymers containing epoxyalkoxy groups of a greater number of carbonatoms are also suitable. These are prepared by substituting forepichlorohydrin such representative corresponding chlorides or bromidesof monohydroxy epoxyalkanes as 1-chloro-2,3-epoxybutane,1-chloro-3,4-epoxybutane, 2-chloro-3,4-epoxybutane,1-chloro-2-methyl-2,3-epoxypropane, 1-bromo-2,3-epoxypentane,2-chloromethyl-1,2-epoxybutane, 1-bromo-4-methyl-3,4-epoxypentane,1-bromo-4-ethyl-2,3-epoxypentane, 4-chloro-2-methyl-2,3-epoxypentane,1-chloro-2,3-epoxyoctane, 1-chloro-2-methyl-2,3-epoxyoctane, or1-chloro-2,3-epoxydecane. Although it is possible to usehaloepoxyalkanes having a greater number of carbon atoms than indicatedabove, there is generally no advantage in using those having a total ofmore than 10 carbon atoms.

In addition, the polyepoxides of halo epoxy alkane of the type discussedabove and a polynuclear dihydric phenol of the type above can beemployed. The preferred polyepoxides of this class being thepolyepoxides of epichlorohydrin and bisphenol A, i.e.,2,2-bis(p-hydroxyphenyl)propane.

The composition of the invention may be used for any number of adhesiveapplications where adhesives are used to assemble various componentparts. As mentioned earlier, one preferred application is in theassembly of component parts in hard disk drives such as the adhering ofread/write heads to data storage systems.

Turning to FIGS. 1 and 2, there is shown a exemplary data storage system20 with the cover 23 removed from the base 22 of the housing 21. Thedata storage system 20 typically includes one or more rigid data storagedisks 24 which are stacked coaxially in a tandem spaced relationship,and rotate about a spindle motor 26 at a relatively high rate ofrotation. Each disk 24 is typically formatted to include a plurality ofspaced concentric tracks 50, with each track being partitioned into aseries of sectors 52 which, in turn, are further divided into individualinformation fields. One or more of the disks 24 may alternatively beformatted to include a spiralled track configuration.

An actuator 30 typically includes a plurality of interleaved actuatorarms 28, with each arm having one or more transducer 27 and slider body35 assemblies mounted to a load beam 25 for reading and writinginformation to and from the data storage disks 24. The slider body 35 istypically designed as an aerodynamic lifting body that lifts thetransducer 27 off of the surface of the disk 24 as the rate of spindlemotor 26 rotation increases, and causes the transducer 27 to hover abovethe disk 24 on an air bearing or airflow patterns produced by high-speeddisk rotation. A conformal lubricant may alternatively be disposed onthe disk surface 24 to reduce static and dynamic friction between theslider body 35 and disk surface 24.

In a typical digital data storage system, digital data is stored in theform of magnetic transitions on a series of concentric, closely spacedtracks comprising the surface of the magnetizable rigid data storagedisks. The tracks are generally divided into a plurality of sectors,with each sector comprising a number of information fields. One of theinformation fields is typically designated for storing data, while otherfields contain sector identification and synchronization information,for example. Data is transferred to, and retrieved from, specified trackand sector locations by the transducers being shifted from track totrack, typically under the control of a controller. The transducerassembly typically includes a read element and a write element. Othertransducer assembly configurations incorporate a single transducerelement used to write data to the disks and read data from the disks.

Writing data to a data storage disk generally involves passing a currentthrough the write element of the transducer assembly to produce magneticlines of flux which magnetize a specific location of the disk surface.Reading data from a specified disk location is typically accomplished bya read element of the transducer assembly sensing the magnetic field orflux lines emanating from the magnetized locations of the disk. As theread element passes over the rotating disk surface, the interactionbetween the read element and the magnetized locations on the disksurface results in the production of electrical signals in the readelement. The electrical signals correspond to transitions in themagnetic field.

The composition of the invention may be used to cure thermoset adhesivesin any number of given applications. One preferred application asillustrated above is the application of transducers to the actuator armof a disk drive system. By applying the transducer such as a read-writelead to the actuator arm in the disk drive environment, outgassing oflow molecular weight volatile compounds is reduced thereby reducing thepotential for disk malfunction.

WORKING EXAMPLES

The following working examples are intended to be illustrative of theinvention.

WORKING EXAMPLE 1 Synthesis of Methylphenyl [4-thiophenoxy]phenylsulfonium perchlorate

A 300-mL, three-neck, round-bottom flask, which has a thermometer and N₂gas inlet and is equipped with a Teflon-covered magnetic stirring bar,is charged with methylphenylsulfone (7 g, 50 mmol) and diphenylsulfide(9.3 g, 50 mmol). The reaction mixture is cooled to 0° C.Methanesulfonic acid (100 mL) is added to the reaction vessel. Thetemperature is gradually raised to room temperature over a 30-minperiod. The reaction is continued for 20 h at room temperature. Thereaction mixture is then poured into perchloric acid (60%, 100 mL) andstirred for 1 h at room temperature, and then water (100 mL) anddichloromethane (100 mL) were added. The aqueous layer is extracted withdichloromethane (2×50 mL). The organic layer is dried over anhydroussodium sulfate. After evaporation, a residue is purified byrecrystallization with ether. The solid is dried under vacuum at roomtemperature for 20 h.

WORKING EXAMPLE 2 Synthesis of Phenyl [4-thiophenoxy] sulfoxide

A 200-mL, three-neck, round-bottom, flask which had a reflux condenserand N₂ gas inlet and is equipped with a Teflon-covered magnetic stirringbar, is charged with methylphenyl[4-(thiophenoxy) phenyl] sulfoniumperchlorate (10 g, 24.5 mmol). Pyridine (50 mL) is added at roomtemperature and stirred for 30 min at room temperature. The temperatureis increased to 100° C., and the reaction is continued for 10 min. Thereaction mixture is poured into 10% HCl solution (300 mL) and isextracted with dichloromethane. The product is purified by flash columnchromatography on silica gel using hexane-chloroform (3:1) as theeluent. After evaporation of the solvents, a product is obtained. Theproduct is dried under vacuum at room temperature for 20 h.

WORKING EXAMPLE 3 Synthesis of Phenyl[4-(thiophenpxy)phenyl]sulfide

A 500-mL, round-bottom flask with a Teflon-covered magnetic stirring baris charged with dichloromethane (50 mL), 10% KHCO₃ (43 mL), andphenyl[4-(thiophenoxy)phenyl]sulfoxide (5 g, 17.0 mmol). To the reactionmixture is added bromine (2.72 g, 17.0 mmol) in dichloromethane (50 mL)over a period of 5 min with vigorous stirring. The reaction is continuedfor 30 min. To the reaction mixture is added a KCl saturated solutionand dichloromethane (100 mL). The aqueous layer is extracted withdichloromethane (2×50 mL). The organic layer is washed with water, driedover anhydrous sodium sulfate, and filtered. After recrystallizationfrom ether, the solid is obtained. The solid is dried under vacuum atroom temperature for 20 h and then is used without further purificationfor polymerization.

WORKING EXAMPLE 4 Polymerization ofPhenyl[4-(thiophenoxy)phenyl]sulfoxide

The polymerization of the phenyl[4-(thiophenoxy)phenyl]sulfoxide ispreformed in trifluoro methane sulfonic acid as the solvent. Theviscosity of the reaction mixture gradually increases. The reactionmixture is poured into hexafluoroantimonic acid (60 wt-%) stirred for 1hour at room temperature. After the precipitation in water, thepoly(sulfonium cation) is quantitatively isolated as a resin having theempirical formula, C₁₈ H₁₃ S₂ SbF₆.

The above discussion, examples and embodiments illustrate our currentunderstanding of the invention. However, since many variations of theinvention can be made without departing from the spirit and scope of theinvention, the invention resides wholly in the claims hereafterappended.

I claim as the invention:
 1. A data storage system comprising a harddisk drive, and a polymeric photoinitiator cured adhesive, wherein priorto curing said polymeric photoinitiator has the formula: ##STR17##wherein n=10 to 150; each of a and b are 0-4 and c is 0-5; A is an alkylor aryl group; X is an anion; and each of R, R', and R" is independentlyH or one or more groups substituted onto the respective phenyl, saidsubstituted group selected from the group consisting of a halogen atom,a nitro group, an alkoxy group, a branched or unbranched C₁ -C₁₈aliphatic group, a cyclic hydrocarbon group, an alkyl or aryl groupcontaining one or more heteroatoms, a C₁₋₁₈ aliphatic group having atleast one hydroxyl group; and a C₃₋₁₉ group having a group of --OCH₂ CH₂O--.
 2. The assembly of claim 1 wherein said adhesive comprises an epoxyresin.
 3. A method of preventing outgassing of volatile chemicals in adisk drive environment said method comprising the steps of: (a) applyingan adhesive comprising a polymeric photoinitiator to the disk driveassembly, said polymeric photoinitiator having the formula: ##STR18##wherein n=10 to 150; each of a and b are 0-4 and c is 0-5; A is an alkylor aryl group; X is an anion; and each of R, R', and R" is independentlyH or one or more groups substituted onto the respective phenyl, saidsubstituted group selected from the group consisting of a halogen atom,a nitro group, an alkoxy group, a branched or unbranched C₁ -C₁₈aliphatic group, a cyclic hydrocarbon group, an alkyl or aryl groupcontaining one or more heteroatoms, a C₁₋₁₈ aliphatic group having atleast one hydroxyl group; and a C₃₋₁₉ group having a group of --OCH₂ CH₂O--; and (b) curing said adhesive through the application of U.V.energy.
 4. The method of claim 3 wherein said disk drive assemblycomprises a read-write head affixed to the assembly by an adhesive curedwith said polymeric photoinitiator.
 5. The method of claim 3 whereinsaid adhesive comprises an epoxy resin.
 6. The method of claim 5 whereinsaid photoinitiator is present in said adhesive composition at aconcentration ranging from about 1 to 5 wt-%.
 7. The method of claim 3wherein said polymeric photoinitiator has a formula wherein each of R,R', and R" is independently selected from the group consisting ofhydrogen, a branch or unbranched C₁₋₄ alkyl group and mixtures thereof,and A is a C₁₋₆ alkyl group.